Field of the Invention
This invention is concerned with improving the adhesive bonding of elastomer or plastic rubber materials based on diene monomers, hereinafter "rubber substrates", to other substrates. For example, improved adhesive bonding is desired in the shoe industry in particular as well as in other industries where rubber substrates are adhesively bonded to other like or unlike substrates. The term "rubber substrate" is used hereinafter in the general sense to include any rubber materials based on diene monomers. Examples of such materials are the following:
______________________________________ SBR (styrene-butadiene copolymer) NR (natural rubber) NBR (acrylonitrile-butadiene copolymer) BR (polybutadiene) BIIR (bromoisobutene-isoprene copolymer) CIIR (chloroisobutene-isoprene copolymer) CR (polychloroprene) IIR (isobutene-isoprene copolymer) IR (polyisoprene) ______________________________________
Adhesive bonding to such materials typically requires a pretreatment or surface treatment such as by oxidation to provide an acceptable bond. This is sometimes referred to as "priming" the plastic substrate surface but is also described as a "surface treatment". New more effective compositions for surface treatment are always desired. However, it is also desirable to identify those compositions which are not noxious or have other negative handling characteristics.
Current surface treatment compositions in use today include dichlorodimethylhydantoin in CH.sub.2 Cl.sub.2 and trichloroisocyanuric acid (TCICA) in ethyl acetate. These compositions are corrosive, require organic solvent and can liberate chlorine on reaction, none of which are desirable. Additionally, they tend to dissolve some plastic substrates and in some cases even attack the adhesive and also present disposal problems.
The previously used aqueous based surface treatment compositions for improving adhesion to rubber materials commercially has consisted of acidified solutions of sodium hypochlorite which is not favored due to release of toxic chlorine gas from the solution.
This invention has discovered that the use of monopersulfate compound (MPS) has many advantages for surface treatment. MPS is available commercially from Du Pont under the trade name OXONE, and has been typically utilized in cleaning and sanitizing formulations.